LT1243 Datasheet | Linear Technology

LT1241 Series High Speed Current Mode Pulse Width Modulators Features s s s s s s s s s s DESCRIPTIO s s Low Start-Up Current: < 250µA 50ns Current Sense Delay Current Mode Operation: To 500k Hz Pin patible with UC1842 Series Undervoltage Lockout with Hysteresis No Cross-Conduction Current Trimmed Bandgap Reference 1A Totem Pole Output Trimmed Oscillator Frequency and Sink Current Active Pull-Down on Reference and Output During Undervoltage Lockout High Level Output Clamp: 18V Current Sense Leading Edge Blanking APPLICATI s s Off-Line Converters DC/DC Converters , LTC and LT are registered trademarks of Linear Technology Corporation. The LT ®1241 series devices are 8-pin, fixed frequency, current mode, pulse width modulators. They are improved plug patible versions of the industry standard UC1842 series. These devices have both improved speed and lower quiescent current. The LT1241 series is optimized for off-line and DC/DC converter applications. They contain a temperature-pensated reference, high gain error amplifier, current sensing parator and a high current totem pole output stage ideally suited to driving power MOSFETs. Start-up current has been reduced to less than 250µA. Cross-conduction current spikes in the output stage have been eliminated, making 500k Hz operation practical. Several new Features have been incorporated. Leading edge blanking has been added to the current sense parator. Trims have been added to the oscillator circuit for both frequency and sink current, and both of these parameters are tightly specified. The output stage is clamped to a maximum VOUT of 18V in the on state. The output and the reference output are actively pulled low during undervoltage lockout. BLOCK DIAGRA REFERENCE ENABLE 5V REF MAIN BIAS REFERENCE PULL-DOWN RT/CT OSCILLATOR T S R 6 OUTPUT P FB 1 1m A 2 2.5V 5.6V 1V - + 2R - R BLANKING + 1.5V ISENSE 3 UV LOCKOUT 8 7 VREF VCC OUTPUT PULL-DOWN 5 18V GND + - 1241...